In certain electronic display equipment, such as a cathode ray tube enclosure, it is required to provide a viewing window having desired optical characteristics, such as good light transmission, reduced glare, and reflection, etc., while also incorporating in such windows electromagnetic shielding characteristics to prevent or reduce the transmission of any electromagnetic energy in the microwave frequency range through the window.
One type of presently available electromagnetically shielded viewing window incorporates a knit wire mesh sandwiched between two layers of glass or plastic panels. The type of shielding mesh chosen generally constitutes a compromise between a desired mass of highly conductive screening across the window opening so as to provide maximum electromagnetic shielding and a desired maximum amount of viewing capability through the window, unobstructed by the shielding screen. Typically, such shielding meshes comprise a loose knit mesh of approximately 18 openings per inch which is formed from a loosely knit mesh with a wire diameter ranging from 0.001-0.005 inch diameter. Typically, grounding of the mesh material is provided by a wire gasket contacting the mesh screen around the perimeter of the viewing window with the wire gasket in turn contacting a metallic window frame in the enclosure. In view of the light reflective characteristics of the embedded metallic mesh, it is often necessary to apply a coating or finish to the glass or plastic window. As an example, when utilizing an electromagnetically shielded viewing window of this type in front of a display element, such as a cathode ray tube, it is often necessary to apply a coating to the glass or plastic panels to increase the contrast between the cathode ray tube display characters and the shielding mesh background.
Thus, the desirable characteristics of an electromagnetically shielded viewing window require a design compromise between the use of a highly conductive screen to provide the most efficient electromagnetic shielding protection; a fairly substantial open area of shielding mesh to enable maximum light transmission through the mesh; and the need for a non-glare or non-reflective viewing surface. It is therefore desirable to provide an electromagnetically shielded viewing window incorporating the most highly attainable characteristic of optical transmission, electromagnetic shielding, and anti-reflection in a viewing window constructed with the same or less cost than in the prior art.